[Bug]: Footer waveform is not aligned with the lane waveforms above it #371

Problem

The footer's waveform strip runs the full width of the window, but the lane
waveforms above it start after the 300px stems/mixer panel. The same moment
in the song therefore sits at two different x positions in the two strips,
and neither ruler's ticks line up with the other's.

Measured at a 1600px window (footer spanning 390→1600):

The strip started 281px too far left and stopped 19px short. The two rulers
also disagreed on tick times: the lanes ruler steps 15/30/60s
(0:00, 0:30, 1:00…) while the footer ruler used eight even slices
(0:00, 0:18, 0:37…).

Reading a position across the two strips — which is the whole point of having
an overview strip under a zoomed lane view — meant eyeballing a 281px offset.

What it should be

The footer laid out on the same column grid as the studio above it:

• Everything time-related (control clusters, waveform, ruler, detection note)
  starts exactly where the lane waveforms start and runs flush to the window
  edge, as they do.
• Both rulers share one tick-step calculation, so a time is labelled at the
  same x in each.
• The column width lives in one variable rather than being hardcoded per
  component, so the two can't drift apart again.
• The left column under the mixer carries the track identity (art, title,
  meta, favourite, export) rather than being blank space.

Limitation

Alignment holds at fit-zoom. Below ~720px of lane width the lanes zoom and
scroll independently while the footer strip always shows the whole song, so
the two can only share a left edge there.

Notes

Addressed in #369.